In wireless communication networks, recent developments of the 3GPP Long Term Evolution, LTE, facilitate accessing local IP based services in the home, the office, in public hot spot or even in outdoor environments. One area in which the access and local connectivity of these local IP based services may be used is in the direct communication between wireless devices in the close proximity of each other. In this case, close proximity may typically refer to less than a few tens of meters, but sometimes even up to a few hundred meters.
This direct mode or Device-to-Device, D2D, communication may demonstrate a number of potential gains over traditional cellular communication. This is because D2D devices are much closer to one another than other cellular devices that have to communicate via a cellular access point, e.g. a radio network node such as an eNodeB.
However, it should be noted that it is preferable to maintain the control of the D2D communication from a network point of view in order to ensure an efficient use of resources and interference handling.
In these mixed cellular and D2D wireless communication networks, it has been suggested to locate D2D communication on cellular uplink, UL, resources in a way such that Time-Division Duplex, TDD, is the duplex transmission scheme of the D2D communication. This means that the cellular UL resources would be allocated for D2D communication transmission in both upstream and downstream directions between each D2D pair of wireless devices in a Time-Division Multiplexed, TDM, manner.
Once the wireless devices discover the proximity of each other, the wireless devices and/or the network may initiate the establishment of the D2D link between the two wireless devices. This is commonly referred to as D2D bearer establishment, and will not be discussed further herein.
However, upon having established the D2D link between the two wireless devices, there is a problem of how to handle the D2D communication when one of the wireless devices is moving out of the cellular coverage of its current cell and into the cellular coverage of another cell, i.e. during a handover. Thus, there is a need to provide way of handling a D2D communication during handover of wireless device in a wireless communications network.
WO2011/109027 A1 describes a handover of a D2D pair of wireless devices between different cells. However, in this case, both of the wireless devices of the D2D pair are part of the handover and the network control of the D2D communication may simply pass from network node of the source cell to the network node of the target cell.